1. Field of the Invention
The present invention relates to a special type bearing device making use of a new type of high-tech eco-material (state-of-the-art material having excellent ecological adaptability) which is different from conventional industrial material in that biomass resources are utilized.
2. Description of the Related Art
For conventional special type bearing devices, copper-based or iron-based sintered alloys, polymer resin materials (nylon, Teflon, other synthetic resin, and so forth), and non-ferrous materials, such as phosphor bronze, brass and so forth, have been in widespread use, however, each of these materials have its own problem.
Conditions required of special type bearing devices include a small friction coefficient, low susceptibility to the effect of temperature, in fabrication, low cost, and slight offensiveness towards mating members.
None of the various conventional materials described above can satisfy all these conditions as required.
For example, the copper-based sintered alloy is soft, and has a large friction coefficient, so that it is susceptible to the effect of change in temperature while its wear resistance is less than satisfactory depending on its application.
The iron-based sintered alloy has problems in that it is inferior in affinity and conformability with mating members, incapable of raising its oil retention ratio to a sufficiently high level, has a high expansion coefficient and so forth.
As for the polymer resin material, it is in principle intended for use in the case of dry friction where no lubricating oil is used, and its application is limited to the cases of use under a light load, use in a dry condition, and so forth. Further, it has problems such as limitations to enhancement of friction coefficient as well as wear resistance besides a problem of thermal expansion.
Meanwhile, the non-ferrous material described above can exhibit a function of satisfactory lubrication in its application under a high load, at low revolutions and so forth, however, it is not necessarily satisfactory in respect of friction coefficient, and wear resistance.
Now, an attempt to obtain a porous carbonaceous material by utilizing rice bran, produced in quantity of 900,000 tons a year in Japan and in as much as 33 million tons a year throughout the world, has been well known by researches carried out by Mr. Kazuo HOKKIRIGAWA, the first inventor of the present invention (refer to xe2x80x9cFunctional Materialxe2x80x9d, May issue, 1997, Vol. 17, No. 5, pp. 24xcx9c28).
Herein are disclosed a carbonaceous material (referred to hereinafter as RB ceramic) obtained by mixing degreased bran derived from rice bran with a thermosetting resin before, kneading, drying a formed kneaded mixture obtained by pressure-forming a kneaded mixture, and subsequently, firing the formed kneaded mixture as dried in an inert gas, and a method of producing the carbonaceous material.
With such a method as described above, however, it has been practically difficult to form the formed kneaded mixture with high precision because there occurs discrepancy in dimensions by as much as 25% in terms of a contraction ratio of the dimensions of a finished formed product obtained after firing in the inert gas to those of the formed kneaded mixture prepared by pressure-forming.
It is therefore an object of the invention to solve drawbacks of the conventional special type bearing units described above, and to provide a special type bearing device capable of satisfying all the requirements as described, that is, a special type bearing device that is insusceptible to damage, is light in weight, has a long service life and excellent wear resistance, is insusceptible to the effect of variation in temperature, is easy to fabricate, and has little offensiveness towards mating members, the special type bearing device further being capable of sufficiently retaining a lubricant such as oil and grease, and retaining the lubricant for a long period of time without the need of supplying oil during operation, thereby being rendered maintenance-free.
A new class of ceramic (CRB ceramic) as described later, representing further improvement on RB ceramic, is a ceramic material friendly to nature, obtained by using rice bran as a raw material, and by mixing degreased bran derived from the rice bran with a thermosetting resin before firing. CRB ceramic has the following excellent features:
very high hardness
very small expansion coefficient
porous organization structure
good electrical conductivity
small specific gravity and light weight
a very small friction coefficient
excellent wear resistance
easy to mold or to form in a die
a small contraction ratio of the dimensions of a finished product to those of a formed workpiece
ceramic material having varying-features can be produced by mixing with a variety of resins
the raw material being rice bran, there is little adverse effect on global environment, leading to conservation of natural resources.
Accordingly, it can be said that this ceramic material has conditions suitable for application to a special type bearing device, such as insusceptibility to damage, light weight, a long service life, capability of retaining oil and grease for a long period of time, and so forth.
The ceramic (CRB ceramic) described above is an improved material of RB ceramic, that is, a black resin or porous ceramic, obtained by mixing degreased bran derived from rice bran with a thermosetting resin before kneading, subjecting a kneaded mixture thus obtained to a primary firing in an inert gas at a temperature in a range of 700 to 1000xc2x0 C., pulverizing the kneaded mixture after the primary firing into carbonized powders passing through a 100-mesh sieve, mixing the carbonized powders with a thermosetting resin before kneading, pressure-forming a kneaded mixture at pressure in a range of 20 to 30 MPa, and subjecting a formed workpiece thus obtained again to a heat treatment in an inert gas atmosphere at a temperature in a range of 100 to 1100xc2x0 C. CRB ceramic differs largely from RB ceramic in that in contrast with RB ceramic having a contraction ratio of the dimensions of a finished product thereof to those of a formed workpiece at as high as 25%, CRB ceramic has a very small contraction ratio at not more than 3%, rendering it superior to RB ceramic.
The inventor has discovered that special type bearing devices having a variety of features can be fabricated with ease by applying CRB ceramic as material for at least a part of the respective special type bearing devices.
In another aspect of the present invention, the dimensions of a workpiece already formed of RB ceramic can be properly adjusted by shaving the same although the conventional RB ceramic has a contraction ratio of the dimensions of a finished product thereof to those of the workpiece already formed at as high as 25%, and therefore, the invention does not exclude embodiments thereof, using RB ceramic. Because RB ceramic has substantially the same property as that of CRB ceramic except in respect of the dimensions of the finished product thereof, the invention does not exclude embodiments thereof, using RB ceramic, in this regard either.
In carrying out the invention, however, it is preferable to use mainly CRB ceramic because a product of high-precision dimensions can be obtained through one forming process in this case.
Further, it has been discovered that special type bearing devices having a variety of features can be fabricated by introducing novel configurations to contact parts of the system as well as by suitable combination of material used for a conventional special type bearing device made of synthetic resin with material used for a conventional special type bearing device made of steel based metal.
More specifically, the invention provides a special type bearing device comprising an axis, a rotating body or rotating bodies, fixedly attached to the axis or formed integrally therewith, and a supporting body with which the rotating body or the rotating bodies are in contact, wherein at least a part of the axis, the rotating body or the rotating bodies, and the supporting body is made of RB ceramic or CRB ceramic.